Almond growers learn about weed-control options

When it comes to controlling weeds, almond growers and pest control advisors have a lot of options. University of California Cooperative Extension researchers conduct trials to help determine the most effective herbicides.

UCCE weed specialist Brad Hanson has been conducting research at the Nickels Soil Lab in Arbuckle, and he reported on the research projects at a recent field day at Nickels.

The first project used 10 different herbicide treatments. Nine of the treatments are with registered products and one is not currently registered, but should be by the end of the year, Hanson said.

• Treatment 1—Burndown only using Rely and glyphosate, Roundup PowerMAX;
• Treatment 2—Grower standard treatment: GoalTender and Surflan or Goal Surflan;
• Treatment 3—Pindar GT;
• Treatment 4—Chateau 12-ounce rate;
• Treatment 5—Matrix full rate;
• Treatment 6—Alion 3 ½-ounce rate;
• Treatment 7—Matrix and Alion 2-ounce rate;
• Treatment 8—Alion 3 ½-ounce rate and Matrix 4-ounce rate;
• Treatment 9—Split application, Alion in winter and Prowl in spring;
• Treatment 10—Broadworks herbicide.

Pindar GT in Treatment 3 has been registered now for about five years, and it's a combination product, meaning it has a mixture of two different modes of action, Hanson said.

"This is a good product with a broad weed spectrum, especially on broadleaves, but it picks up a lot of grasses as well," Hanson said.

A few of the plots in the Treatment 4 Chateau applications are starting to break. It's mostly where workers have walked across the berms and basically disturbed that herbicide layer, he said.

The full rate of Matrix in Treatment 5 is really one of the cornerstone products in orchard weed management, Hanson said.

Matrix has been around a long time, and it's sometimes used by itself, but more commonly as a tank-mix partner, and it brings a lot to the table as a tank-mix, he said.

"In a wetter year, or a wetter situation, it often doesn't last long enough into the spring," Hanson said.

A lot of PCAs and growers are using a cut rate of Matrix as was done in Treatment 7, but Hanson doesn't recommend it. The lower rates of Alion and Matrix will not give dependable weed control year in and year out as a full rate would, he said.

"There's a reason that rate was set at 4 ounces," Hanson said, adding that "that's probably one of the best treatments out here."

The split application in Treatment 9 used Alion in January and then, in early April, two quarts of Prowl was applied, Hanson said.

"I've been looking at that sequential application because we're seeing more and more issues with summer grasses in orchards—Junglerice, barnyard grass, and as you go farther south sprangletop, witchgrass," Hanson said.

"I think that we're asking a lot with our December/January application to control grasses that are coming up in May, June and July," he said.

When there is rainfall, or if micro- or solid-set sprinklers are available, an application of Surflan or Prowl late in the spring could provide better grass weed control in the summer, Hanson said.

Treatment 10 used Broadworks, the new herbicide that is expected to receive registration soon, so it will be available for the dormant application late in 2015, Hanson said.

"I think this is going to be an excellent tank-mix partner for a lot of our orchard weed managers," he said.

Hanson said he has been very impressed with Broadworks' activity with hairy fleabane and horseweed, as well as a number of other broadleaf weeds.

"It has some postemergent activity, but its strength is really the pre-emergent timing. And I think that's going to be a good tank-mix partner," Hanson said.

Caio Brunharo, a doctoral candidate in weed science at UC Davis, also did a test site for Broadworks at the Nickels Soil Lab.

"The purpose of this trial was to test Broadworks as a tank-mix to other herbicides that are being commonly used for almonds," Brunharo said, adding he found Broadworks had good control for hairy fleabane, horseweed and starthistle.

Hanson has another project underway at Nickels that looks at the effects of glufosinate or Rely-type herbicides on young almond trees.

"When Rely and the glufosinate herbicides were first registered, growers and PCAs were using them like they were Gramoxone," Hanson said.

They were treated like they were only contact materials and not translocated like paraquat or Shark, but that's not quite true, Hanson said.

While glufosinate doesn't translocate as well as glyphosate, it does translocate a lot more than paraquat or some of the true contact materials, he said.

Hanson initiated the project after some growers reported damage on the lower part of the trunk on young trees—first-leaf, second-leaf, sometimes third-leaf trees, he said.

"A lot of what I saw in the field seemed to be associated with potentially high applications—overlaps, handgun applications where the guys are out there hosing these weeds down at the base of the tree," Hanson said.

Using a single nozzle sprayer, herbicide treatments were applied to the east side of the tree from ground level to about 18 inches high.

"Basically, we just sprayed one side of the tree," Hanson said, "on three different varieties—Nonpareil, Aldrich and Sonora."

Hanson's take-home message—be very cautious about applications on young trees, and don't take the cartons off any sooner than you have to, particularly on first-leaf trees, maybe even second-leaf trees.

"Big trees are pretty forgiving of sloppy applications of any herbicide. Our small trees are much less forgiving. Make sure you do a good job of application—not overdosing the trees," Hanson said.

"This isn't just a Rely question, this is a glufosinate question," he said, adding that any of the glufosinate herbicides will probably have the same potential for injury as Rely.

"On those young trees, I would err on the low side of the label rate, or be cautious, I guess, of using it on those really young trees," Hanson said.

(Kathy Coatney is a reporter in Corning. She may be contacted at kacoatney@gmail.com.)